Existing Code Division Multiple Access (CDMA)-based cellular network technologies achieve what is often referred to as uplink macro-diversity through the use of the well-known “soft handoff” mechanism. In soft handoff mechanism, uplink frames at the link layer or Media Access Control (MAC) sublayer that are transmitted by a user's wireless communication device or mobile terminal are received at multiple base station transceivers as controlled by a separate controlling element, e.g., a Radio Network Controller (RNC) or Base Station Controller (BSC), which is typically more centrally located in the radio access network. The set of receiving base station transceivers forward the uplink frames to the controlling element, which then uses techniques such as frame selection or soft combining, as well as automatic repeat request (ARQ) mechanisms in an attempt to reconstruct and correctly receive the frames sent from the user's wireless communication device. This design has evolved primarily in support of circuit-switch applications, e.g., voice, and is not well-suited for packet-switched networking/internetworking. The concentration of information through the controlling element reduces network scalability and also increases the reliability requirements, and cost, of the controlling element. The design also imposes timing, synchronization, and communication latency requirements between the base station transceivers and/or between the base station transceivers and the controlling element.
These requirements are overly restrictive for many packet-switched network/internetwork technologies. In connectionless, packet-switched networks/internetworks such as those based on the Internet Protocol (IP), a sequence of packets (or packet flow) sent from a source node to a destination node need not follow the same path throughout the network/internetwork. It is also generally desirable to confine the dynamics of a specific air-link interface technology to the interface itself, thereby allowing network layer intelligence to be brought forward to the edge of the fixed infrastructure.
Internet Protocol Overview
IP technology is designed to enable packet-switched interconnection of a heterogeneous set of computer communication networks. A potentially diverse set of network and link layer technologies are interconnected through gateways (or routers) that provide a packet forwarding service. Information is transferred from sources to destinations as blocks of data called datagrams, where sources and destinations (or hosts) are identified by fixed length addresses. Routing in IP internetworks is connectionless in nature, in that datagrams are forwarded between routers on a hop-by-hop basis using the destination address in the datagram. Each router makes an independent next-hop forwarding decision using its own internal forwarding table. IP also provides for fragmentation and reassembly of long datagrams, if necessary, for transmission through “small packet” networks. In some IP internetworks there is relatively little distinction between hosts and routers. Herein, when no distinction is required the term “node” will be used. One distinction that generally holds true is that while any IP node may send and receive datagrams, only routers forward datagrams.
In a common case a host has only one connection (or interface) to the internetwork. When the interface is point-to-point in nature, the decision regarding the next-hop to which datagrams from the host should be sent is trivial. Typically, a default route designates the remote end of the point-to-point link as the next-hop for all outgoing datagrams from the host. Alternatively, when the interface is broadcast in nature, such as with a direct connection to a Local Area Network (LAN), the next-hop decision for the host is more complex. In this case a contiguous set of addresses is typically associated with nodes directly connected via the interface (a “subnet”). Thus, if an outgoing datagram is destined for a node on the directly connected subnet (e.g., the destination address is within the interface address space), the datagram is sent directly to the corresponding node, otherwise the datagram must be sent to a router on the directly connected subnet for forwarding. In general there may be more than one router on the subnet and a host may use different routers as the next-hop depending on the destination address of the datagram. However, in many cases a host will simply designate one router as a default next-hop and direct all outgoing datagrams (that are not destined for a node on the directly connected subnet) to that default router. Finally, a host may be multihomed, wherein it has more than one interface that provide connectivity to the internetwork. Each interface may have an associated set of addresses that corresponds to directly connected nodes. Outgoing datagrams destined to a directly connected node are sent to the node on the associated interface. Other outgoing datagrams may be directed either to a specific next-hop router based on the destination address of the datagram or to a default router. The next-hop decision for a router is much the same as that described for a multihomed host. The primary difference being that a router must make such a decision for both datagrams sourced by the router and datagrams being forwarded by the router.
IP Internetworking over Wireless Communication and Networking Technologies
Connectivity between nodes in an IP internetwork can be provided by both wired and wireless communications and network technologies. Wireless communication and network technology can be used to provide connectivity either directly between IP nodes that have wireless communication device interfaces or through non-IP wireless link-layer devices, such as a wireless access point serving as a bridge between a wireless LAN and a hardwired LAN. In any case, channel conditions, spatial relationships, and other factors have a significant impact on physical and link layer connectivity, which makes these link connections more dynamic and time varying than in hardwired networks.
Before packets, e.g., IP datagrams, can be transmitted between two wireless communication devices, a viable communication connection must be established. The process of establishing a wireless communication connection may progress through a series of possible stages as follows.                1. In the first stage, which may be referred to as “physical layer synchronization”, devices typically detect one another based on physical layer mechanisms and synchronize with one another to allow further communication.        2. In the second stage, which may be referred to as “physical layer access exchange”, the devices typically exchange a series of physical layer signals or control messages to enable access to air-link resources. After this stage, the devices can send and receive link layer control messages.        3. In the third stage, which may be referred to as “link layer exchange”, the devices typically exchange a series of link layer control messages. This may include tasks such as authentication, authorization, registration and establishment of keys for enciphering and deciphering link traffic. After this stage, the devices can send and receive link layer data messages. Thus, the connection is capable of supporting the exchange of network and higher layer control and data packets (e.g., IP datagrams).        4. In the fourth stage, which may be referred to as “network layer exchange”, the devices typically exchange network and higher layer control messages. This may include tasks such as address resolution, network layer admission control, internetwork routing, and negotiating quality of service. Depending on the specifics of the network/internetwork scenario, various control traffic exchanges in this fourth stage may be required before exchange of general IP data traffic is supported (particularly data traffic that must traverse more than one network hop).        
Note that some of the message exchanges may directly or indirectly involve entities such as Authentication, Authorization and Accounting (AAA) servers other than the wireless communication devices and the entities that encompass them (particularly in the third and fourth stages above).
In some instances a communication connection may be more specifically described as either a physical-layer connection or a link-layer connection. While the specific attributes and differences may vary depending on the particular communication technology and/or protocols, the former loosely corresponds with the end of the second stage and the later with the end of the third stage. Since a link-layer connection is typically associated with link-layer functions such as message framing and ARQ, which need not be closely coupled to a particular physical layer connection, it is possible that in some communication systems a link-layer connection may include, or operate over, multiple physical layer connections. When higher layer packets are transmitted over a physical-layer or link-layer connection, they are typically partitioned into one or more frames, where each frame may include some additional header information. Depending on the underlying technology and/or protocols, frames may be either fixed or variable in length.